May 5, 2014
Environmental Factors As Influential As Genes In Autism Spectrum Disorders
redOrbit Staff & Wire Reports - Your Universe Online
While experts typically focus on genetic factors when analyzing the causes of autism spectrum disorders (ASD), new research appearing in the Journal of the American Medical Association (JAMA) has found that environmental factors are equally as important.
In the study, Dr. Sven Sandin of the Karolinska Institutet in Sweden and colleagues from the US and UK set out to determine the heritability of autism and the risk among family members. They also attempted to assess the importance of genetic factors versus environmental ones by reviewing the data of the more than two million children born in Sweden between the years of 1982 and 2006.
Dr. Sandin’s team determined the relative recurrence risk (RRR), or the odds that autism will be diagnosed in a participant who had a sibling, half-sibling or cousin who had been diagnosed with the neurodevelopmental disorder. Overall, the study looked at 14,516 children with ASD, of which 39 percent (5,689) were diagnosed with autism.
They found that kids who have a brother or sister with ASD were 10 times more likely to receive a similar diagnosis, compared to 3 percent for those with half-brothers/sisters that had ASD, and 2 percent for those with cousins. The pattern was described as being similar for autistic disorder, but with a slightly higher magnitude.
Environmental factors were split into two categories: shared environments (those shared between family members, such as socioeconomic status) and non-shared environments (those unique to each individual, such as birth complications or medication taken during pre or perinatal periods). Those conditions unique to each patient, the non-shared environments, were the major source of environmental risk for the purposes of this study.
While most previous research has suggested that the heritability of autism spectrum disorders could be as high as 80 percent to 90 percent, the new study – described by King’s College London, one of the institutions involved in the research, as “the largest and most comprehensive to date,” estimates it to be 50 percent, with the other 50 percent explained by non-heritable or environmental factors.
“We were surprised by our findings as we did not expect the importance of environmental factors in autism to be so strong,” explained study author Professor Avi Reichenberg of the Mount Sinai Seaver Center for Autism Research. “Recent research efforts have tended to focus on genes, but it's now clear that we need much more research to focus on identifying what these environmental factors are.”
“Our study was prompted by a very basic question which parents often ask: 'if I have a child with autism, what is the risk my next child will too?' Our study shows that at an individual level, the risk of autism increases according to how close you are genetically to other relatives with autism,” Dr. Sandin added. “We can now provide accurate information about autism risk which can comfort and guide parents and clinicians in their decisions.”